Conversion of Peanut Trypsin-Chymotrypsin Inhibitor B-III to a Chymotrypsin Inhibitor by Deimination of the P₁ Arginine Residues in Two Reactive Sites

Abstract

The deimination of the arginine residues in peanut trypsin-chymotrypsin inhibitor B-III caused the disappearance of its trypsin-inhibitory activity. Peanut protease inhibitor B-III was incubated with peptidylarginine deiminase, resulting in the conversion of 2.5 mol of arginine to citrulline and in the loss of its trypsin-inhibitory activity. However, the ability of the deiminated inhibitor to inhibit chymotrypsin was as strong as before. Structural analysis of the deiminated B-III indicated that the P₁ arginine residues at both reactive sites, Arg (10) and Arg (38), were completely modified to citrulline by the action of peptidylarginine deiminase, and that the Arg (60) in the C-terminal region of B-III was partially deiminated. These residues seem to be exposed on the surface of the molecule. The P₁' arginine residue at the first reactive site, Arg (11), was not deiminated at all.